SIX MONTHS AFTER SEPT. 11, AMERICA HAS TAKEN THE FIGHT TO AL-QAEDA. BUT BEHIND THE SCENES, THE CIA AND FBI HAVE BEEN IN A DESPERATE SCRAMBLE TO FIX A BROKEN SYSTEM BEFORE ANOTHER STRIKE COMES. AS OUR

For a few harrowing weeks last fall, a group of U.S. officials believed that the worst nightmare of their lives--something even more horrific than 9/11--was about to come true. In October an intelligence alert went out to a small number of government agencies, including the Energy Department's top-secret Nuclear Emergency Search Team, based in Nevada. The report said that terrorists were thought to have obtained a 10-kiloton nuclear weapon from the Russian arsenal and planned to smuggle it into New York City. The source of the report was a mercurial agent code-named DRAGONFIRE, who intelligence officials believed was of "undetermined" reliability....